Synthesis and Characterization of New Open-Framework Vanadium

Mar 22, 2010 - Fuzhou 350108, P. R. China, and §Department of Chemistry, Jinggangshan University, Ji'an,. Jiangxi 343009, P. R. China. Received May 8...
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DOI: 10.1021/cg900502y

Synthesis and Characterization of New Open-Framework Vanadium Tellurite Featuring an Unprecedented (3,7)-Connected Network: K3[(VVO4)(VIVO)4(TeO3)4] 3 4H2O†

2010, Vol. 10 2021–2024

Xi-He Huang,*,‡ Chang-Cang Huang,*,‡ Dong-Sheng Liu,‡,§ Zhong-Qian Liu,‡ and Yu-Bo Wang‡ ‡

State Key Laboratory Breeding Base of Photocatalysis, Department of Chemistry, Fuzhou University, Fuzhou 350108, P. R. China, and §Department of Chemistry, Jinggangshan University, Ji’an, Jiangxi 343009, P. R. China Received May 8, 2009; Revised Manuscript Received March 4, 2010

ABSTRACT: Hydrothermal reaction of TeO2, V2O5, K2C2O4, H2C2O4 in water yielded a novel vanadium tellurite, K3[(VVO4)-

(VIVO)4(TeO3)4] 3 4H2O. The compound exhibits ¥2[V4Te4O18]4- puckered anionic layers that are pillared by [VO4]3- units into a threedimensional inorganic open framework with unprecedented (3,7)-connected (43)2(46 3 610 3 85) topology.

Dedicated to Prof. Xin-Tao Wu on the occasion of his 70th birthday. *To whom correspondence should be addressed. E-mail: xhhuang@fzu. edu.cn (X.-H.H.); [email protected] (C.-C.H.)

indicates the potential for a variety of open-framework topologies. Furthermore, it has been reported that the asymmetric coordination environment of Se(IV) and Te(IV) ions can induce noncentrosymmetric structures with interesting physical properties, such as nonlinear optical second harmonic generation (SHG).12 In our previous work, we have successfully obtained several metal selenites and tellurites.13 As a continuous work, we have attempted to design novel materials by combining the oxy-anions of tellurium(IV) and vanadium. Herein, we report the hydrothermal synthesis and characterization of a new vanadium tellurite, K3[(VVO4)(VIVO)4(TeO3)4] 3 4H2O (1). Although several vanadium tellurites have been reported,10a,13b,13d,13e,14 only one organically templated vanadium tellurite with 3D open-framework structure has been reported hitherto.10a The title compound is an inorganic species and presents a novel example of a 3D openframework vanadium tellurite. Compound 1 was synthesized from the hydrothermal reaction15 of TeO2, V2O5, K2C2O4, H2C2O4, and H2O in a molar ratio of 2:1:2:0.5:330 at 170 C for 4 days and isolated as black blocked crystals by hand from unidentified black powder. The oxidation states for vanadium atoms of 1 were proven to be tetra- and penta- valence by X-ray structural analysis, which is consistent with the coloration of the crystal. The assignment of oxidation states for vanadium atoms is confirmed by bond valence sums, the EPR, and UV-vis diffuse reflectance spectra (vide infra). The C2O42- anion is necessary in the preparation process of 1. When using VOSO4 and V2O5 as the vanadium source, various reactions with different stoichiometries, temperatures, and reaction times only produced black powder. Moreover, our limited attempts to prepare the title compound by addition of various amounts of reducing reagent NH2OH 3 HCl to replace the C2O42anion into the reaction system were unsuccessful. Single-crystal X-ray diffraction analysis16 reveals that 1 crystallized in orthorhombic space group Pmmn. There are two crystallographically unique V centers, two unique Te atoms, and three unique Kþ ions in the asymmetric units (Figure 1). Both Te atoms are located on the mirror plane (Wyck. Code 4f), whereas the V(1) center and three Kþ ions sit in the higher symmetric position, i.e., Wyck. Code 2b, 2a, 2b, 2a for V(1), K(1), K(2), and K(3), respectively, and the V(2) atom is in the general position. Compound 1 exhibits a novel 3D anionic open-framework, formed by TeO3 pyramids, VO4 tetrahedra, and VO6 octahedra via the corner- and/or face-sharing mode. As shown in Figure 1, the V(1) site shows a slightly distorted tetrahedral coordination

r 2010 American Chemical Society

Published on Web 03/22/2010

Open-framework and microporous solids have found widespread applications in catalysis, absorption, ion exchange, and so forth.1 These important materials have been extended to a variety of chemical compositions, because the utility of these materials is intimately correlated to their compositions. A large number of open-framework silicates, phosphates, germanates, borates, phosphites, and sulfates have been reported in the past two decades.1c,e,2 Recently, there has been an increasing interest in the use of vanadium-centered polyhedra as building units for the construction of open-framework materials.3 The vanadium is particularly interesting owing to its variability oxidation states and different coordination geometries, such as tetrahedron, square pyramid, and octahedron.3-6 Vanadium-based catalysts are known to be effective for oxidation chemistry due to the accessibility of multiple oxidation states.5 The isomorphous substitution of vanadium into the zeolite lattice to obtain catalysts with efficient activity in selective oxidation of different organic molecules such as hydrocarbons or alcohols has also been reported.5b,6 On the other hand, a novel class of open-framework solids containing so-called lone-pair ions, characterized by unusual stereochemical effects of its lone-pair electrons (LPEs), such as As3þ, Se4þ, Te4þ as building units has also received great current interest.7,9 Chemically, the stereochemically active LPEs might play a role as an invisible structure directing agent. The entire structure is greatly affected by the requirement for “empty” space to accommodate the lone pair electrons, which reduces generally the structural dimension of their metal compounds.8 Openframework metal selenites have received a certain amount of attention, and some progress has been made in the synthesis of open-framework metal selenites.1c,2h,9 Compared with the great attention-getting of metal selenites, studies on the tellurium(IV) analogue are still limited. So far, only one naturally existing tellurite mineral, zemannite, and a handful synthetic metal tellurites with a three-dimensional (3D) open-framework structure have been reported.10 However, contrast to the selenium(IV) ion, which often adopts the pyramidal coordination, the tellurium in the þ4 oxidation state is found in a host of coordination environments, such as pyramidal “TeO3”, seesaw “TeO4”, and square pyramidal “TeO5” geometry.11 The variety of coordination chemistry of tellurium(IV) and vanadium suggests that a great deal of flexibility in many framework architecture is possible and †

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Figure 1. Local structure of 1 with atom labeling (50% probability ellipsoids). Symmetry code: (a) x, 0.5 - y, z; (b) x, 1.5 - y, z; (c) -x, 0.5 þ y, 1 - z; (d) -x, 0.5 þ y, 2 - z; (e) 0.5 - x, 1.5 - y, z.

Figure 2. View of the structure of 2D ¥2[V4Te4O18]4- anionic layer along the (a) a-axis, (b) b-axis. The polyhedra colored in cyan represent the [V(2)O6] octahedra. The ellipsoid colored in blue connecting with Te atoms represent the lone pair of electrons of Te atoms.

geometry with two terminal oxygen (O(7) and O(7e)) and two bridging oxygen (O(5) and O(5e)) atoms. The V(1)-O(7) and V(1)-O(5) bond lengths are 1.625(5) and 1.820(4) A˚, and the O-V-O angles of the V(1)O4 unit are 113.4(3), 107.4(1), respectively. The V(2) atom exhibits a distorted octahedral environment. The terminal oxo strong bond of V(2)-O(1) (1.613(3) A˚) implies a typical vanadyl group (VdO). The longest V-O bond of the V(2)-centered octahedra of 2.257(3) A˚ are involving in the O(6c) which shows the strong trans effect, while the other V(2)-O bond lengths involving the equatorial plane range from 1.960(3) to 2.070(3) A˚. The cis and trans O-V-O bond angles of the [V(2)O6] octahedron range from 72.1(2) to 104.3(2) and from 156.7(2) to 170.6(2), respectively. The geometry of Te(1) and Te(2) centered polyhedra can be explained by VSEPR theory as [TeO3E] tetrahedral, of which the lone pair electron (denoted as E) occupies the apex position. The Te-O bond lengths vary from 1.874(4) to 1.896(4) A˚, and the O-Te-O angles are in the range of 93.8(2)-97.8(2). The distinct coordination polyhedra around the V(1) and V(2) centers suggest their oxidation states of þ5 and þ4, while both Te atoms in the oxidation states of þ4. The bond valence study17 for V(1), V(2), Te(1), and Te(2) give values of 5.15, 4.04, 3.87, and 3.80, respectively, which confirms the valence state of these ions in the crystal structure. Two [V(2)O6] octahedra are held together by sharing O(4d), O(5), and O(6c) to produce a mirror-symmetric dimeric [V2O9] moiety. These [V2O9] moieties arrange as discontinuous columns parallel to the b-axis, and are connected by [TeO3] units resulting in a 2D ¥2[V4Te4O18]4- puckered anionic layer paralleling to the bc plane (Figure 2). In the anionic layer, each [V2O9] moiety

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Figure 3. View of the ¥3[V5Te4O20]3 inorganic framework along the b-axis. The polyhedra colored in purple represent the [V(1)O4] tetrahedra.

connects with six [TeO3] units while each [TeO3] unit linked with three [V2O9] moieties. The LPEs of Te(IV) atoms are located in the concave of the puckered anionic layer. The [V(1)O4] tetrahedra between the anionic layers adopt a μ2-connected mode and incorporate the adjacent anionic layers into a 3D pillar-layered 33 open-framework (Figure 3). The inorganic frame¥ [V5Te4O20] work has 1D linear 12-ring channels running along the [010] direction. The opening of the 12-ring channel is approximately elliptical in shape and delimited by six [VO6] tetrahedra, four [TeO3] pyramids, and two [VO4] tetrahedral with an approximate free-pore diameter of 3.1-5.7 A˚. A PLATON18 analysis, performed only on the inorganic framework, suggested a solventaccessible volume of approximately 26.6%. Three symmetrically unique Kþ ions and one unique H2O molecule locate in the framework channels (Figure S1, Supporting Information). All of the Kþ ions are coordinated to 8-10 oxygen atoms, from the adjacent anionic layers and water molecules, in the distance of 2.761(4)-3.262(3) A˚ with irregular polyhedral shape. The water molecule is coordinated to the K(1) and K(2) ions. Two hydrogen-bonding interactions involving the water molecule and O(3) and O(7) atoms are observed with O 3 3 3 O distances of 2.778(5) and 2.817(4) A˚, and O-H 3 3 3 O angles of 143.0(5) and 160.0(7). Our limited attempts to synthesize congeneric open-framework through replacing the Kþ ion for Naþ and NH4þ ions were unsuccessful. Only one 1D vanadium(V) tellurites NaVTeO5 and two polymorphs of layered mixturevalence vanadium(IV/V) tellurites with NH4þ as countercation were obtained. The results imply that the unique connected mode of compound 1 and the presence of K-O bonds and hydrogen bonds might play an important role in the formation of the title vanadium tellurite open-framework. A prominent structural feature of compound 1 is the observation of an unprecedented (3,7)-connected network. Topologically, the [TeO3] pyramids and the dimeric [V2O9] moiety can be defined as a 3- and 7-connected node, respectively, and the μ2bridging [VO4] tetrahedron as a linker connecting two 7-connected nodes. On the basis of this simplification, the framework of compound 1 can be reduced as a binodal net topology. This net (denoted as kvt implies the topology found in this potassium vanadium tellurite) can be specified by the vertex symbol of (43)2(46 3 610 3 85) and long Schl€ afli symbol of (4 3 4 3 4)2(4 3 4 3 4 3 4 3 4 3 4 3 62 3 62 3 62 3 62 3 62 3 62 3 62 3 62 3 62 3 62 3 88 3 88 3 88 3 88 3 88) (Figure 3). It should be noted that structures incorporating high-connected node (more than six) remain largely unexplored, and only one (3,7)-connected network according to the RCSR database (http://rcsr.anu.edu.au/), namely, bcl, has been reported to date. Thus, the (43)2(46 3 610 3 85) network represents so far the second example of a (3,7)-connected network. An EPR spectrum and UV-vis diffuse reflectance spectrum (Figure S2 and S3, Supporting Information) were measured in

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Figure 4. The (43)2(46 3 610 3 85) network of compound 1.

solid state at room temperature. The EPR spectrum shows one V4þ signal with g = 1.9674, suggesting that the single d-electron was restricted in the V(2) center. Two broad UV-vis absorption bands at approximately 798 and 635 nm correspond to the promotion of the single electron of the [VIVO6] octahedron from the dxy orbital to the dyz or dxz orbital.19 This degeneracy with a large energy difference of about 3200 cm-1 may due to the lower symmetry of the strongly distorted [VIVO6] octahedron. The dxy to dx2-y2 transition at approximately 508 nm is not well-resolved but is visible as a shoulder. The dxy to dz2 transition with higher energy is probably obscured by the LMCT absorption of O f VIV, O f VV, and O f TeIV, which were observed as the strong absorption bands with overlapping maxima at about 379, 427, and 464 nm, and one shoulder band at 268 nm. Thermogravimetric analysis (TGA) studies of 1 were performed under N2 from 50 to 800 C at a 10 C/min rate. The result (Figure S4, Supporting Information) shows that there are three weight loss processes. The first weight loss in the range of 190-290 C should correspond to the removal of lattice water. However, the observed mass loss (2.8%) is much lower than the expected value (calcd 5.6%). The lower reduction in mass loss was likely due to the loss of the volatile lattice water below 50 C. There is no significant weight loss within the temperature range 295-500 C. Beyond 500 C, compound 1 undergoes two weight loss processes, implying the collapse of the framework of 1. In summary, we have synthesized and characterized a novel mixed valence vanadium tellurite. The compound possesses a 3D inorganic open-framework containing V(IV), V(V), and Te(IV) centered polyhedra as building units. The network of the compound exhibits an unprecedented (43)2(46 3 610 3 85) topology and represents the second example of a (3,7)-connected network reported so far. Acknowledgment. Financial support was received from the Innovation Fund for Young Scientist of Fujian Province (2008F3059). Supporting Information Available: X-ray crystallographic data in CIF format, material and instruments, figures of the coordination geometries of K ions and water molecule, figures of EPR, IR and UV-vis diffuse reflectance spectra, and TGA of compound 1. This information is available free of charge via the Internet at http:// pubs.acs.org/.

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and our group. (d) Huang, X.-H.; Liu, Z.-Q.; Huang, C.-C.; Shen, L.-J.; Yan, X.-B. Acta Crystallogr. 2009, C65, M404. (e) Huang, X.-H.; Liu, Z.-Q.; Huang, C.-C.; Shen, L.-J.; Yan, X.-B. Acta Crystallogr. 2009, C65, M385. (14) (a) Xiao, D.; Li, Y.; Wang, E.; Wang, S.; Hou, Y.; De, G.; Hu, C. Inorg. Chem. 2003, 42, 7652. (b) Xie, J.-Y.; Mao, J.-G. Inorg. Chem. Commun. 2005, 8, 375. (c) Feng, M.-L.; Mao, J.-G. J. Solid State Chem. 2005, 178, 2256. (d) Rozier, P.; Vendier, L.; Galy, J. Acta Crystallogr. 2002, C58, i111. (e) Harrison, W. T. A.; Buttery, J. H. N. Z. Anorg. Allg. Chem. 2000, 626, 867. (f) Grzechnik, A.; Halasyamani, P. S.; Chang, H.; Friese, K. J. Solid State Chem. 2009, 182, 1570. (g) Jiang, H.; Huang, S.; Fan, Y.; Mao, J.; Cheng, W. Chem.;Eur. J. 2008, 14, 1972. (h) Laval, J. P.; Boukharrata, N. J. Acta Crystallogr. 2009, C65, i1. (i) Johnston, M. G.; Harrison, W. T. A. Acta Crystallogr. 2007, C63, i57. (j) Pitzschke, D.; Jansen, M. Z. Anorg. Allg. Chem. 2007, 633, 1563. (k) Zhang, D.; Johnsson, M. Acta Crystallogr. 2009, C65, i9. (15) A mixture of TeO2 (0.322 g, 2.0 mmol), V2O5 (0.182 g, 1.0 mmol), K2C2O4 3 H2O (0.369 g, 2.0 mmol), and H2C2O4 3 2H2O (0.063 g, 0.5 mmol) in 6 mL water was heated in a 15 mL capacity Teflonlined reaction vessel at 170 C for 4 days. After slow cooling to room temperature over a period of 24 h, a black crystalline product of compound 1 in a yield of 11% (0.055 g), as well as an unidentified black powder were obtained. IR (KBr pellet, ν/cm-1): 3481(s), 3413(s), 1647(m), 1622(m), 1400(m), 978(s), 962(s), 948(vs), 928(s), 782(m), 733(m), 669(vs), 510(s), 413(m). (16) Crystal data for 1: H8K3O24Te4V5, orthorhombic, space group Pmmn, Mr = 1274.46, a = 16.8856(7) A˚, b = 7.5479(11) A˚,

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c = 8.9037(4) A˚, V = 1134.78(18) A˚3, Z = 2, Dc = 3.730 g 3 cm-3, F(000) = 1160 and μ = 7.680 mm-1. T = 293(2) K. Data collections of 1 were performed with MoKa radiation (λ = 0.71068 A˚) on a Rigaku R-axis RAPID diffractometer. A total of 10703 reflections were collected in the range of 2.29 e θ e 27.49, of which 1453 (Rint = 0.0776) were independent, final R1 = 0.0280 for 1324 reflections with I > 2σ(I), and ωR2 = 0.0665, GOF = 1.000 for all 1453 data. The structure was solved by direct methods and expanded using Fourier techniques. Non-hydrogen atoms are refined anisotropically, and the hydrogen atoms were refined isotropically. All calculations were performed using SHELXS97 and SHELXL97 programs.20 Further details of the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (fax: (þ49) 7247-808-666; e-mail: [email protected]) on quoting deposition number CSD-420796. (a) Brown, I. D.; Shannon, R. D. Acta Crystallogr. 1973, A29, 266. (b) Brown, I. D.; Altermatt, D. Acta Crystallogr. 1985, B41, 244. Spek, A. L. PLATON: A Multi-Purpose Crystallographic Tool; Utrecht University: Utrecht, Netherlands, 2001. (a) Dutta, S. K.; Kumar, S. B.; Bhattacharyya, S.; Tiekink, E. R. T.; Chaudhury, M. Inorg. Chem. 1997, 36, 4954. (b) Hagen, H.; Barbon, A.; Faassen, E. E. V.; Lutz, B. T. G.; Boersma, J.; Spek, A. L.; Koten, G. V. Inorg. Chem. 1999, 38, 4079. Sheldrick, G. M. SHELXL97 and SHELXS97: Program for X-ray Crystal Structure Solution and Refinement. University of G€ottingen: G€ottingen, Germany, 1997.